1) Technical Field
The subject invention relates to a robotic manipulator for grasping, separating and transporting a single sheet of material from a stack of material to a drop-off zone.
2) Description of the Prior Art
Various machines and de-stackers have been contemplated by the prior art for grasping, separating and transporting a single sheet of material from a stack of material. The stacks of material may include thin sheets of metal, such as steel or aluminum, thin sheets of plastic, glass plates, corrugated paper, lumber, wall and roofing panels or other like workpieces. During the lifting and separating of the sheets, many of these articles have a tendency to stick together due to vacuum pressure. Hence, a user may have difficulty separating the sheets such that more that one sheet of material is transported at a time.
To add to the difficulty, the thin sheets of metal are typically surface treated with oil or grease. In addition, during the stacking of the sheets, the air between adjacent sheets is usually expelled by the weight of the metal sheets. Thus resulting in the formation of a continuous film of lubricating material between adjacent metal sheets which acts as a glue between the sheets. This problem is particularly prevalent in such industries as the automotive industry in which many products are manufactured from metal sheets in a relatively rapid succession. The individual sheets must be quickly unstacked and fed one at a time into production presses.
To overcome the difficulties associated with de-stacking these sheets, in particular thin metal sheets, the prior art has developed several different methods and apparatuses. One known method is to incorporate a plurality of suction cups in which some of the suction cups may be raised to bend the top sheet of metal and to then separate the top sheet from the stack of material. This separation may also be assisted by dispensing air near the separation point. Examples of these types of de-stacking apparatuses are disclosed in U.S. Pat. Nos. 3,826,485; 4,081,085; 5,207,553; and 5,609,377. These prior art solutions have been only moderately effective and fail to provide satisfactory, rapid and reliable separating and transporting of the single sheets of material.
A robotic manipulator having a gripping tool assembly for separating an uppermost sheet of material from a stack of material. The assembly comprises a lift arm and a frame fixedly mounted to the lift arm. At least one separating device is movably mounted to the frame for grasping and lifting a peripheral portion of the uppermost sheet of material to create an initial separation of the uppermost sheet of material from the stack of material. At least one stationary suction lifter is fixedly secured to the frame for grasping and lifting the remaining portions of the uppermost sheet of material after the initial separation of the uppermost sheet of material. The gripping tool assembly is characterized by first and second air hoses or nozzles mounted to the frame with the first air nozzle positioned above the second air nozzle whereby the first air nozzle provides pressurized air toward the periphery of the uppermost sheet of material to assist in the initial separation of the uppermost sheet of material and the second air nozzle provides pressurized air below the uppermost sheet of material after the initial separation of the uppermost sheet of material.
The subject invention also includes the method of separating the uppermost sheet of material from the stack of material comprising the steps of; affixing the stationary suction lifters to the uppermost sheet of material, affixing the separating device to the uppermost sheet of material, actuating the separating device to lift the peripheral portion of the uppermost sheet of material to create the initial separation between the uppermost sheet and the stack of material, and the method is characterized by dispensing pressurized air toward the periphery of the uppermost sheet of material simultaneously with the actuating of the separating device and dispensing pressurized air below the uppermost sheet of material after the initial separation of the uppermost sheet of material.
Accordingly, the subject invention includes a method and apparatus which effectively separates a single sheet of material from a stack of material by utilizing a pair of air nozzles working in conjunction with the separation device. As will be discussed in greater detail below, the subject invention also incorporates a number of other devices to ensure that only one sheet of material is separated and lifted from the stack of material.